Road-weary Beth pays an overdue visit to her older sister Ellie, who is raising three kids on her own in a cramped L.A. apartment. The sisters' reunion is cut short by the discovery of a mysterious book deep in the bowels of Ellie's building, giving rise to flesh-possessing demons, and thrusting the sisters into a primal battle for survival as they’re faced with the most nightmarish version of family imaginable.